Graphene is a single layer of carbon atoms densely packed in a honeycomb crystalline-lattice configuration. This atomic configuration gives rise to a high current-carrying capacity, excellent thermal conductivity, and low-voltage operational potential. Graphene therefore possesses the properties to be an excellent component of integrated circuits. For example, graphene has a high charge-carrier mobility as well as low noise, allowing it to be used as a channel in a field-effect transistor (FET). Development of epitaxial graphene FETs on the wafer scale is highly desirable for future graphene electronics.
Commercial and military interest in graphene-based electronic components includes sophisticated imaging systems as well as radar and communications applications, which have been hindered by component cost, limited resolution, and high power dissipation. A graphene platform could revolutionize these applications because of graphene's electrochemical properties and low cost, allowing for scalability and system-wide integration of graphene-based components.
To realize graphene-based circuits, various types of graphene are needed. Modulation of the electrical properties of graphene is of great technological importance. Doping graphene with other elements is a promising way to modulate electrical properties. Theoretical studies and experiments have shown that doping graphene can tailor the physical and chemical properties of graphene and open possibilities of new chemistry and new physics on graphene.
Doping is a common approach to tailor the electronic properties of semiconductor materials. Graphene is readily p-doped (positive charge carriers) by adsorbates, but for device applications, it would be useful to generate n-doped graphene. Up to now, most researchers have studied n-doped graphene using nitrogen.
For example, in “Synthesis of N-Doped Graphene by Chemical Vapor Deposition and Its Electrical Properties” by D. Wei, et al. (Nano Letters, vol. 9, No. 5, pages 1752-1758, March 2009), it is disclosed that ammonia may be introduced to synthesize substitutionally doped graphene at temperatures around 800° C. Other references discussing N-doping with nitrogen include “Electrical Properties of Nitrogen-/Boron-Doped Graphene Nanoribbons With Armchair Edges”, by S. S. Yu, et al. (IEEE Transactions on Naotechnology, Vol. 9, No. 1, pages 79-81, January 2010); “Nitrogen-doped graphene and its electrochemical applications” by Y. Shao, et al. (Journal of Materials Chemistry, 20, 7491-7496, June 2010); and “Synthesis, Structure, and Properties of Boron- and Nitrogen-Doped Graphene”, by L. S. Panchakarla, et al. (Advance Materials, 21, 4726-4730, 2009). These references do not describe or suggest n-type doping of graphene with phosphorus atoms or with phosphorus-containing molecules or fragments.
What are needed are practical methods for n-type doping of graphene, either during graphene synthesis or following the formation of graphene. There is a need in the art for n-doped graphene for various electronic-device applications.